Large optical telescopes are used to view astronomical objects such as stars and galaxies. Such telescopes collect data for measurement and scientific analysis. A representation of an optical telescope is shown in FIG. 1. Light from the stars, or other astronomical objects, 100 is reflected by a mirror 102 in the telescope onto the focal surface of the telescope 104. The light received at the focal surface is captured by optical fibres and fed to a spectrograph 106 for analysis. In large optical telescopes several hundred optical fibres are used to capture the light.
The spectrum of light emitted by astronomical objects provides information about many attributes of the object, including composition, age, position in its life time and movement of the object relative to the earth. The more light that is captured from a particular object, the more efficiently information can be determined about that object. Optical spectrum analysis can be complicated and hindered by light from other sources and so, in order to analyse the spectrum of an object most reliably and efficiently, the optical fibres used for collection of the light should be physically aligned with the incoming light as accurately as possible. This requires significant precision control when positioning the optical fibres.
Additionally, due to the constant rotation of the earth, the position of a particular object in the sky will vary over time. In order to remain aligned with incoming light from an object, large optical telescopes require the ability to reposition the light capturing optical fibres accurately and efficiently.
In typical large optical telescope systems, the mirrors used to capture and reflect the light have a diameter of several meters. These mirrors reflect the light onto a focal surface of around 0.5 meters diameter or more. The typical cross section diameter of a light capturing optical fibre is around 100 micrometers and the positional accuracy required in order to collect the light for analysis is single micrometers.
FIG. 2 is a representation of a plate of optical fibres for capturing light in a large optical telescope. The plate 200 includes around 3000 optical fibres 204. Each optical fibre is contained within a separate tube 202 for support and positioning. For many astronomical research programs using optical telescopes, the position of each optical fibre should be controlled independently and be able to move independently of all other fibres. In some systems, the positioning of each optical fibre is controlled by independent piezoelectric actuators associated with each optical fibre.
There are many design considerations when designing systems to position large numbers of optical fibres. One challenge is the close proximity of the fibres and their actuator units, specifically that the position of each fibre must not be affected by movement of adjacent fibres or actuators. This is important, in particular due to the required positional accuracy of within a few micrometers. A further challenge lies in controlling the movement of all fibres simultaneously, so that all fibres can be positioned reliably and accurately in short time frames. The minimum achievable precision is a particular challenge due to the long length of the fibre compared with the positional accuracy requirements (a few micrometers) on that fibre. For a ‘tilting spine’ design as shown in FIG. 2, the supporting tubes must be long to reduce the tilt of the fibre tip when each fibre is moved to the limits of its positioning range.
In certain fibre positioning systems in optical telescopes, each individual fibre is positioned via a magnetic interaction with a magnetic mount. This large number of magnetic materials in such a confined space generates complicated magnetic field patterns.
In certain systems, piezo electric actuators are used to control the positioning. Typically, the actuators require electric potentials of hundreds of volts to produce deformation of the material. With each piezoelectric actuator being driven independently, this creates significant considerations for electrical connections to those crystals in such confined locations.
Embodiments of the present address these problems.